1. Technical Field of the Invention
This invention relates to a self-centering device for locking the wheel rim for the purpose of mounting or removing its tyre.
2. Prior Art
To lock the wheel rim in the working position, tyre removal machines are currently provided with suitable devices, known as self-centering devices, which generally comprise a circular plate provided with a series of radial grooves within which sliding blocks having locking heads (fasteners) which lock the wheel rim in the working position are made to slide. The locking heads, generally four in number, are equidistant about a circumference, and are of the double acting radial sliding type, in order to be able to grip the wheel rim both from the outside and from the inside.
The circular plate is rotated about itself by a coaxial shaft driven by a suitable motor unit.
The sliding blocks are caused to slide within the grooves by a double-acting cylinder-piston unit positioned coaxial to the shaft and acting on levers connected to the sliding blocks, as described in greater detail in Italian utility model No. 224593 in the name of the same Applicant.
In mounting or removing a tyre onto or from the wheel rim, only one side of the tyre at a time can be operated on, i.e. after operating on one side of the wheel rim, this has to be rotated through 180xc2x0.
This both demands physical force from the operator and results in an extension of the operating time.
On the other hand, those systems which lock the wheel at the hub, and which allow access to both sides of the wheel at the same time, present the drawback of insecure wheel locking against rotation, which is often precarious.
The object of the invention is to overcome the drawbacks of the known art within the framework of a rational and reliable solution.
The invention attains said object by providing a device for locking the wheel rim at the hub, comprising means for rotating the wheel even if considerable tangential resistance forces are present.